1. Technical Field
The present disclosure relates to a turbo equalizer that uses a noise variance estimation value and a wireless receiving apparatus that includes the turbo equalizer.
2. Description of the Related Art
A turbo equalizer has a strong equalizing capability for multipath inter-symbol interference (ISI). A known type of turbo equalizer that can reduce an operation amount of ISI equalization is a turbo equalizer that has a frequency domain soft canceller followed by minimum mean squared error (MMSE) filter. In combination with the sum-product decoding method, a low density parity check (LDPC) code has an excellent correcting capacity that approaches the Shannon limit. The sum-product decoding method calculates the likelihood of all data bits in a decoding process, and does not require re-encoding in a process of generating soft replicas in repetitive processing of turbo equalization. Therefore, the LDPC code can be said to be an error correcting code suitable for the turbo equalizer.
In the turbo equalizer that has the frequency domain soft canceller followed by MMSE filter and uses the LDPC code, a noise variance (see Japanese Unexamined Patent Application Publication No. 2006-54900) of a received signal is used to calculate a coefficient for the MMSE filter and calculate a logarithm of likelihood ratio (LLR) to be given to an LDPC decoder. The accuracy of estimating a noise variance affects reception performance.